Reconquest of the Water 



mowing down every year those very reeds and grasses 

 which are all-important to its success. 



One sees the same processes at work in every fresh- 

 water stream and in large lochs or small ponds, but not 

 so much in polluted waters. 



We should perhaps try to describe the appearance of 

 the submerged plant world of a small loch as it would 

 affect those weird, large-eyed crustacean larvae or in- 

 choate caddis-worms which browse upon the surface. 

 This surface itself may be mud, but towards the top it 

 is a very loosely piled up, water-saturated material. 

 But even if the bottom consists of stones, rock, or 

 sand, it is sure to be everywhere covered over by a 

 shimmering indistinct mistiness of a rich golden brown 

 colour. That is due to millions of diatoms and other 

 minute algae. The former are attached by transparent 

 stalks of jelly and arranged in chains or bands, or 

 sometimes each has its own elegant little stalk. 



Crossing the water there may be perhaps the gigantic 

 rhizome and roots of a reed or grass, or the stout cable 

 of a water-lily leaf. Upon these grow many sorts of algae. 

 Some form vivid dark-green coils and festoons, waving 

 freely in the water ; there may be twined and entangled 

 masses of Spirogyra with its brilliant green ribbons, or 

 the emerald star-like chloroplasts of Zygnema. Here 

 perhaps one may find a tiny, branched Chaetophora, 

 ^ of an inch in height with the habit of a broom ; there 

 the great cable of a water-lily leaf is plastered over by 

 rosettes of Coleochaete. Here may be a mass of bright 

 clear jelly full of blue-green cells. Through the water 

 floats majestically flaring green Desmids, which may be 

 like crescents, rosettes, or fringed triangles. There are 

 battalions of diatoms, also some free, others in chains 

 or bands. At some seasons other algae suddenly appear 

 in myriads. 



137 



